I will give a short summary, The LM317 here configured for around 6.4V DC. The Q3 BC547 limits the current, you can select R3 to suit, make it 1/2W. The Ni-Cd battery pack 1.2 * 4 will not get Over-Current or Over-Voltage due to this circuit.

The IRF540 Mosfet or any other equivalent you have around, along with Q2 BC547 forms a current source for the parallel 12 LED array. Ultra-bright White LED at 20mA each or use a 1W ready LED Chip. R4/R6 can be selected for the Max LED current.

This is an electronic choke for a Conventional Fluorescent Lamp. This was an application note of MJE13005 a High Voltage Switching NPN Power Transistor. I Might have modified it. This was very popular in the early days, The Coil Winding and Ferrite is very Critical design.Emergency Light with Fluorescent Tubes

The diodes, npn transistor and caps are high voltage 350V-1KV, The tubelight is 40W-60W 5 feet long. This circuit replaced the choke and starter in an existing frame.

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